We report an open-label case series of six male inpatients (mean age=29.8 years, SD=9.1) who had minimal or no response to antipsychotic treatment throughout 6 weeks of treatment and were not given clozapine for various reasons. Written informed consent was obtained in all cases. All patients were taking the maximum tolerated dose of the respective antipsychotic drug with sufficient plasma levels (initial treatment: one taking olanzapine, 20 mg/day; one, amisulpride, 600 mg/day; four, quetiapine 500–900 mg/day). They were monitored with use of the Brief Psychiatric Rating Scale (BPRS). Oxcarbazepine was added to antipsychotic treatment, starting with 300 mg/day and ending with a final dose of 900 to 2100 mg/day (mean=1500 mg/day, SD=465), with a transient headache as a side effect in a single case.